Compounds of the formula (I) are known and can be employed as plant protection agents having a herbicidal action (see, for example, WO 92/00304, DE-A1-4236902, WO 89/10921, EP-A1-301784, EP-A1-187489). That is, compounds of formula (I) are sulfonylurea herbicides.
Known processes for the preparation of compounds of formula (I) often have disadvantages. For example, many of the known processes for the preparation of compounds of formula (I) obtain the compounds only in poor yields, especially if sparingly soluble heterocyclic amine components are required. Other processes are undesirably multi-stage processes or, in some cases require the use of highly toxic chemicals (such as, for example, phosgene) or of hazardous reagents (such as, for example, alkali metal hydrides), such that, for safety reasons, particular precautions must be taken when carrying out these processes on a large industrial scale. Moreover, poor yields, or having to undergo multi-stages (multi-steps or "pots"), or having to undertake particular safety precautions due to the need for using highly toxic chemicals or hazardous reagents, present increased costs. Thus there are economic disadvantages from prior processes for preparing compounds of formula (I).
Processes for obtaining the sulfonylurea herbicides of formula (I) involve the reaction of sulfonamides of the formula A--SO.sub.2 --NH.sub.2 and carbamates of the formula Ar--O--CO--NR--B, in which Ar is an aromatic radical and A, B and R have the meanings given therefor in formula (I) (see, for example, the patent publications cited above). If the preparation of the carbamates is included in the process, this variant usually also has disadvantages because strong bases, which are difficult to handle, must be employed. For example, the "carbamate" process of EP-A-562576 for the preparation of sulfonylurea herbicides requires sodium hydride as the base. Therefore, the "carbamate" process has disadvantages which include having to undertake safety precautions due to the use of a hazardous reagent, sodium hydride, and the attendant high expenditures (costs) involved with a process involving this hazardous reagent.
Accordingly, it would be desired to provide a process for the preparation of sulfonylurea herbicidal compounds of the formula (I) which overcomes one or more of the disadvantages of prior processes. For instance, it would be desired to provide a process for the preparation of formula (I) compounds which avoids the multi-stages of previous processes, or which avoids the use of highly toxic chemicals or of hazardous reagents of prior processes. And, it would be a great advance in the art to provide a process which avoids the multi-stages and the use of highly toxic chemicals and/or hazardous reagents of prior processes.